1. Field of the Invention
The present invention relates to polyimide-based polymers containing dianhydride moieties having a particular structure in the repeating units thereof, and/or copolymers of the polyimide-based polymers. The present invention also relates to a positive type photoresist composition comprising at least one of the polyimide-based polymers and/or copolymers thereof as a binder resin to achieve high resolution, high sensitivity, excellent film characteristics and improved physical properties.
2. Description of the Related Art
With the recent trend toward higher integration, higher density, higher reliability and higher speed of electronic devices in the field of semiconductors and semiconductor devices, particularly, liquid crystal display devices, considerable research efforts have been made to utilize the inherent advantages of organic materials that are easy to process and purify. However, organic polymers for use in the field of semiconductors and semiconductor devices should be thermally stable even at temperatures as high as 200° C. in the device fabrication processes.
Polyimide compounds have good thermal stability and excellent mechanical, electrical and chemical properties. These advantages have extended the application of photoresists and photosensitive insulating films including polyimide compounds to the field of semiconductors and displays. Under these circumstances, there is a need for polyimide-based polymer compounds that do not undergo film reduction and swelling in the formation of fine patterns, which have previously not been required in conventional polyimide photoresists.
A polyimide polymer is typically prepared by two-step polycondensation of a diamine and a dianhydride in a polar organic solvent, such as N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc) or dimethylformamide (DMF) to obtain a polyimide precursor solution, coating the polyimide precursor solution on a silicon wafer or glass, and curing the coating by baking. Commercially available polyimide products for electronic materials are supplied in the form of polyimide precursor solutions or polyimide films. Polyimide precursor solutions are main forms of polyimide products supplied in the field of semiconductor devices.
Polyimide resins are applied to the production of buffer coating films of semiconductor devices. In a large-scale integrated (LSI) circuit, volume shrinkage of a resin after packaging and thermal stress arising from the difference in the coefficient of thermal expansion between a chip and the resin induce cracks in a passivation film of the chip and damage to metal interconnections. In an effort to solve such problems, a buffer layer composed of a polyimide is formed between the chip and the packaging material. The buffer layer should be as thick as 10 μm to perform its role. The thicker the buffer layer, the better the buffering effect, leading to an improvement in the yield of semiconductor products.
A polyimide layer requires the formation of fine patterns, such as electrode interconnections and wire bonding pads. Via holes are formed in the polyimide layer by coating a photoresist on a conventional non-photosensitive polyimide film, followed by etching. In recent years, many attempts have been made to apply photosensitive polyimides to the formation of via holes. The use of a conventional non-photosensitive polyimide requires etching for processing holes through a photoresist to bond wires and connect metal interconnections, whereas the use of a photosensitive polyimide can eliminate the need for lithography using a photoresist. In the latter case, the buffer coating process is shortened by about 50%, resulting in productivity improvement and cost reduction. The final step of the semiconductor device fabrication process is also shortened, greatly contributing to an improvement in production yield.
Research is being actively undertaken on positive type photosensitive polyimides rather than on negative type photosensitive polyimides for the following reasons.
The first reason is that a positive type photosensitive polyimide has a higher resolution than a negative type photosensitive polyimide. The second reason is that a positive type photosensitive polyimide is exposed in a relatively small area, compared to a negative type photosensitive polyimide, indicating low possibility of defects. The third reason is that the use of a negative type photosensitive polyimide causes problems in terms of production cost and environmental pollution (e.g., waste water treatment) because it requires an organic solvent such as N-methyl-2-pyrrolidone (NMP) or dimethylacetamide (DMAc) as a developer, while the use of a positive type photosensitive polyimide is economically advantageous and environmentally friendly because it requires an alkaline aqueous solution as a developer.
Many methods have been developed to impart polyimide resins with photosensitivity, for example, by chemically bonding cross-linkable functional groups to the polyimide precursors or mixing cross-linkable monomers with the polyimide precursors, in order to use the polyimide resins for the preparation of photoresist compositions.
As another example, a quinonediazide compound is added to a polyamic acid, a polyamic ester having acid functional groups in the side chains thereof or a polyimide having acid functional groups in the side chains thereof. However, high solubility of the polyamic acid in an alkaline developer causes the problem of film reduction upon development, which requires the addition of an amine, etc. Further, the polyimide or the polyamic ester has high resolution, but the acid functional groups remain even after curing, causing the problems of high water absorption or poor alkali resistance of the cured film.
Thus, there is an urgent need in the art to develop high-resolution polyimide compounds that do not suffer from film reduction or swelling during fine pattern formation while possessing appropriate solubility in alkaline developers.